“The global climate-science community has indicated that changes of planetary temperature of even 1– 2°C have the potential to bring about significant global exposures to coastal erosion, sea-level rise, water supply and extreme climatic events, to name but a few. The potential number of humans impacted by a 2°C change may count in the hundreds of millions. The European Union has already set a target of maximum warming of 2°C in the belief that warming beyond this represents an unreasonable risk of “dangerous” climate change. Such a change in the average global temperature might be regarded by many as small, but it has the capacity to culminate in major consequences, something that scientists feel is still under-appreciated in both public and private policy development.” — Dr Graeme Pearman, 3 December 2007 (Pearman, 2007).

The rapid Arctic melt now under way consigns the widely advocated 2°C warming cap — always an unacceptable political compromise — to the dust bin because it is demonstrably too high and would eventually be a death sentence for billions of people and millions of species as positive feedbacks work through the climate system. Yet there are now suggestions that we should consider a 3 degrees C warming cap, even though “the Earth’s history suggests that with warming of 2–3°C the new equilibrium sea level will include not only most of the ice from Greenland and West Antarctica, but a portion of East Antarctica, raising sea level of the order of 25 meters. Contrary to lethargic ice sheet models, real world data suggest substantial ice sheet and sea level change in centuries, not millennia. The century time scale offers little consolation to coastal dwellers, because they will be faced with irregular incursions associated with storms and with continually rebuilding above a transient water level” (Hansen, 2006d).

The brutal question is this: do those advocating a 3°C understand in any significant way what 3°C really means? What it means in tangible, physical terms? In the Pliocene, three million years ago, temperatures were 3°C higher than our pre-industrial levels, so it gives us an insight into the 3°C world. The northern hemisphere was free of glaciers and ice sheets, beech trees grew in the Transantarctic mountains, sea levels were 25 metres higher, and atmospheric CO2 levels were 360–400 ppm, very similar to today. There are also strong indications that during the Pliocene, permanent El Nino conditions prevailed. Rapid warming today is already heating up the western Pacific Ocean, a basis for a coming period of “super El Ninos”. Between 2°C and 3°C, the Amazon rainforest, whose plants produce 10% of the world’s terrestrial photosynthesis and which have no evolved resistance to fire, may turn to savannah as drought and mega-fires first destroy the rainforest, turning trees back into CO2 as they burn or rot and decompose.

The carbon released by the forests’ destruction will be joined by still more from the world’s soils, together boosting global temperatures by a further 1.5ºC. It is suggested that in human terms the effect on the planet will be like cutting off oxygen during an asthma attack. A March 2007 conference at Oxford talked about “corridors of probability”, with models predicting the risk of the Amazon passing a “tipping point” at 10–40% over the next few decades.

The UK’s Hadley Centre climate change model, best known for warning of catastrophic losses of Amazon forest, predicts that under current levels of greenhouse gas emissions, the chances of such a drought would rise from 5% now (one every 20 years) to 50% by 2030, and to 90% by 2100.

The collapse of the Amazon is part of the reversal of the carbon cycle projected to happen around 3°C, a view confirmed by a range of researchers using carbon-coupled climate models. 3 degrees C would likely see increasing and significantly large areas of the terrestrial environment being rendered essentially uninhabitable by drought and heat. Rainfall in Mexico and Central America is projected to fall by 50%. Southern Africa would be exposed to perennial drought, a huge expanse centred on Botswana could see a remobilisation of old sand dunes, much as is projected to happen earlier in the US west. The Rockies would be snowless and the Colorado river will fail half the time. Drought intensity in Australia could triple.

With extreme weather continuing to bite — hurricanes may increase in power by half a category above today’s top-level Category Five — worldfood supplies will be critically endangered. This could mean hundreds of millions — or even billions — of refugees moving out from areas of famine and drought in the sub-tropics towards the mid-latitudes. As the Himalayanice sheet relentlessly Climate ‘code red’: The case for a sustainability emergency 30 melts with rising temperatures, the long-term water flows into Asia’s great rivers and breadbasket valleys — the Indus, Ganges and Brahmaputra, the Mekong, Yangtse and Yellow rivers — will fall dramatically. If global temperatures rise by 3°C (and that’s becoming the unofficial target for some rich-country governments), water flow in the Indus is predicted to drop by 90% by 2100. The lives of two billion people are at stake. For all this, 3 degrees C is the cap effectively being advocated by the Australian Labor Party (ALP) in its policy “Labor’s Greenhouse Reduction Target — 60% by 2050 Backed By the Science” released on 2 May 2007 by environment spokesperson Peter Garrett, which advocates a 60% reduction in Australian emissions from 2000 levels by 2050 (Garrett, 2007).

The fully developed 60/2050 goal was first formally articulated by a major organisation in 2000 when it was recommended by the UK Royal Commission on Environmental Pollution, to which the ALP’s policy statement makes reference. However, the core idea — of making a 60% cut in CO2 emissions compared to 1990 levels — was given prominence a decade earlier in the first science assessment of the IPCC. This was not presented as a goal as such but was provided by the scientists to help policy makers calibrate the scale of the challenge (Leggett, 2001).

The immediate source of inspiration for Labor’s 60/2050 target appears to be the advocacy of Sir Nicholas Stern who, when all is said and done, advocated a 3 degrees C target in his 2006 report to the UK government. Stern said that constraining greenhouse gas levels to 450 ppm CO2e “means around a 50:50 chance of keeping global increases below 2°C above pre-industrial [and it] is unlikely that increases will exceed 3 Degrees C”. But, he said, keeping levels to 450 ppm CO2e is “already nearly out of reach” because “450 ppm means peaking in the next five years or so and dropping fast”. In other words, it would require immediate and strong action that Stern judged to be neither politically likely nor economically desirable because he thought that the UK and other western governments would not be prepared to direct sufficient resources to solve the problem. So instead Stern pragmatically says the data “strongly suggests that we should aim somewhere between 450 and 550 ppm CO2e”, but his policy proposals demonstrate that he has the higher figure in mind as a practical goal: “It is clear that stabilising at 550 ppm [CO2e] or below involves strong action… but such stabilisation is feasible” even though “550 ppm is risky”. So his policy framework is focused on constraining the increase to 550 ppm, at which level “there is around a 50:50 chance of keeping increases below 3°C (and it is) unlikely that increases would exceed 4°C” (Stern, 2006a, 2006b).

It is beyond reasonable doubt that Stern identifies a 2ºC cap with 450 ppm CO2e and a 3ºC cap with 550 ppm CO2e, noting that for the latter target “the power sector around the world will have to be at least 60% de-carbonised by 2050 and with a bigger proportion de-carbonised in rich countries” (Stern, 2006a, emphasis added). Stern’s last point is often overlooked. The 60/2050 link to a 3ºC cap was reiterated during Stern’s March 2007 visit to Australia, when he told “The Age” that “It would be a very good idea if all rich countries, including Australia, set themselves a target for 2050 of at least 60% emissions reductions” because “the planet would be left with about 550 ppm of CO2 equivalent by 2050” and this would “leave us roughly a 50/50 chance of being either side of 3ºC above pre-industrial times” (Hannam, 2007).

A number of others have followed in Stern’s footsteps, including ex-ABARE chief Dr Brian Fisher, Australia’s lead delegate to the May 2007 IPCC meeting, who says the 2ºC target, with emissions peaking by 2015, “is exceedingly unlikely to occur… global emissions are growing very strongly… On the current trajectories you would have to say plus 3ºC is looking more likely” (Minchin, 2007b). The shift in the pragmatic goal is plain in the 2007 IPCC Working Group III report. Of the 177 research scenarios assessed for future emissions profiles, only six dealt with limiting the rise to the range of 2–2.4ºC. By contrast, 118 covered the range of 3.2–4ºC, which suggests that the IPCC scientists, following the lead of the politicians, have also largely shifted focus from 2ºC (IPCC, 2007).This whole dialogue about 450 ppm or 550 ppm, 2ºC or 3ºC needs to be considered from two other perspectives: climate sensitivity, and the threat of triggering mass loss of ocean algae.

If we accept the view that long-term climate sensitivity (including “slow” feedbacks) is around 6°C, then a doubling of CO2 levels to 550 ppm will in the end produce a 6°C increase. To be brutal, Stern’s 550 ppm target is a 6°C increase and contemplating a 550 ppm policy target for Australia is setting an equilibrium temperature rise of 6°C as policy. And we know that “the last time the planet was 5°C warmer, just prior to the glaciation of Antarctica about 35 million years ago, there were no large ice sheets on the planet. Given today’s ocean basins, if the ice sheets melt entirely, sea level will rise about 70 meters” (Hansen, 2007e).

And what if a target of 550ppm were to result in the destruction of the ocean’s greatest CO2 sink? In peer-reviewed research published in “Nature”, it was demonstrated that it is likely that when CO2 exceeds 500 ppm, the global temperature suddenly rises 6°C and becomes stable again at this elevated temperature despite further increases or decreases of atmospheric CO2 (Lovelock and Kump, 1994). This contrasts with the IPCC models that predict that temperature rises and falls smoothly with increasing or decreasing CO2. Explaining the research, Lovelock points out that as the ocean surface temperature warms to over 12°C, “a stable layer of warm water forms on the surface that stays unmixed with the cooler, nutrient-rich waters below. This purely physical property of ocean water denies nutrients to the life in the warm layer, and soon the upper sunlit ocean water becomes a desert”, recognized by the clear azure blue, dead water of most of today’s ocean surface. In such nutrient-deprived water, ocean life cannot prosper and soon “the surface layer is empty of all but a limited and starving population of algae”. Algae, which constitute most of the ocean’s plant life, are the world’s greatest CO2 sink, pumping down CO2, as well as contributing to cloud cover by releasing dimethyl sulphide (DMS) into the atmosphere, a gas connected with the formation of clouds and with climate, so that warmer seas and fewer algae will likely reduce cloud formation and further enhance positive feedback. Lovelock says severe disruption of the algae/DMS relation would signal spiralling and irreversible climate change. Algae prosper in waters below 10°C, so, as the climate warms, the algae population reduces.

The modelling of climate warming and regulation by Lovelock and Kump suggests that “as the CO2 abundance approached 500 ppm, regulation began to fail and there was a sudden upward jump in temperature. The cause was the failure of the ocean ecosystem. As the world grew warmer, the algae were denied nutrients by the expanding warm surface of the oceans, until eventually they became extinct. As the area of ocean covered by algae grew smaller, their cooling effect diminished and the temperature surged upwards.” The end result was a temperature rise of 8°C above pre-industrial levels, which would result in the planet being habitable only from the latitude of Melbourne south to the south pole, and northern Europe, Asia and Canada to the north pole (Lovelock, 2006).

So, just as events on the ground compel us to conclude that the cap needs to be substantially less than 1ºC, we are now getting the third degree (in reality, the sixth degree) as 2ºC fades as a supposedly “unrealistic” compromise. Policy and goal-setting seem precariously wedged between scientific need and political “reality”, an ambivalence keenly expressed in Stern’s work.

The science established long ago demanded a cap well below 2°C to avoid dangerous impacts. James Hansen — before the Arctic summer of 2007, which will likely cause a further revision downward in his work — pointed to the need for a cap that was a safe amount less than 1.7°C: “Earth’s positive energy imbalance is now continuous, relentless and growing… global warming of more than 1°C above today’s global temperature [of 0.7°C] would likely constitute ‘dangerous anthropogenic interference’ with climate… This warming has brought us to the precipice of a great ‘tipping point’. If we go over the edge, it will be a transition to ‘a different planet’, an environment far outside the range that has been experienced by humanity. There will be no return within the lifetime of any generation that can be imagined, and the trip will exterminate a large fraction of species on the planet” (Hansen, 2005a, 2008). We have to keep reminding ourselves that Hansen is talking as a scientist; this is not just a rhetorical flourish to enliven his prose. Hansen has also suggested that an increase of “even 1°C [over the present] may be too great” (Hansen, 2007a), and more recently that: “Proxy measures of CO2 amount and climate simulations consistent with empirical data on climate sensitivity both indicate that atmospheric CO2 amount when an ice sheet first formed on Antarctica (34–35 million years before present) was probably only 400–600 ppm. This information raises the possibility that today’s CO2 amount, ~383 ppm, may be, indeed, likely is already in the dangerous range” (Hansen and Sato, 2007b). In court testimony in Iowa, Hansen reaffirmed this view: “I am not recommending that the world should aim for additional global warming of 1°C. Indeed, because of potential sea level rise, as well as the other critical metrics that I will discuss, I infer that it is desirable to avoid any further global warming” (Hansen, 2007e).

But presumably because such a 1.7 ºC (over pre-industrial) cap required drastic, politically challenging action, it was judged “impractical” and a pragmatic, diplomatically acceptable tradeoff of 2°C was agreed upon. Now as emissions grow even more rapidly than expected, the 2°C cap is now looking “impractical” and 3 degrees C hangs in the air as “looking more likely”. One could imagine that in another decade, 3 degrees C will be looking “impractical” and 4ºC will be “looking more likely”. Like heating a frog slowly, 3 Degrees of warming has only one certain outcome.